Multiscale Porous Carbon Materials by In Situ Growth of Metal-Organic Framework in the Micro-Channel of Delignified Wood for High-Performance Water Purification.

Porous carbon materials are suitable as highly efficient adsorbents for the treatment of organic pollutants in wastewater. In this study, we developed multiscale porous and heteroatom (O, N)-doped activated carbon aerogels (CAs) based on mesoporous zeolitic imidazolate framework-8 (ZIF-8) nanocrystals and wood using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation, in situ synthesis, and carbonization/activation. The surface carboxyl groups in a TEMPO-oxidized wood (TW) can provide considerably large nucleation sites for ZIF-8. Consequently, ZIF-8, with excellent porosity, was successfully loaded into the TW via in situ growth to enhance the specific surface area and enable heteroatom doping. Thereafter, the ZIF-8-loaded TW was subjected to a direct carbonization/activation process, and the obtained activated CA, denoted as ZIF-8/TW-CA, exhibited a highly interconnected porous structure containing multiscale (micro, meso, and macro) pores. Additionally, the resultant ZIF-8/TW-CA exhibited a low density, high specific surface area, and excellent organic dye adsorption capacity of 56.0 mg cm-3, 785.8 m2 g-1, and 169.4 mg g-1, respectively. Given its sustainable, scalable, and low-cost wood platform, the proposed high-performance CA is expected to enable the substantial expansion of strategies for environmental protection, energy storage, and catalysis.

Flexible nanocellulose-based SERS substrates for fast analysis of hazardous materials by spiral scanning.

Surface-enhanced Raman scattering (SERS) has proven to be a valuable tool for assessing harmful chemicals in various substances, including water, soil, and foods. However, a fast measurement system is required for multiplexed detection to extend the range of its applications. The rotating scanning stage of the SERS substrate is considered to be a promising approach to achieving a fast measurement system. This paper reports a facile measurement system by using a flexible nanocellulose-based SERS substrate and a spiral scanning system, which rotates the cylinder sample holder and moves the stage. A flexible nanocellulose-based SERS substrate deposited with Au nanoparticles is suitable for the spiral scanning system, which requires SERS substrates to be highly flexible and durable. The well-known toxic fungicide, thiram, was tested by this system. The results revealed that the nanocellulose-based SERS substrate is well-fitted with a spiral scanning system and that the signal data from a large area substrate can be obtained within 30 s. It is noteworthy that the error of spiral scanning measurements is smaller than that of multi-spot sampling. This work provides a powerful tool for Raman spectroscopic analysis, which requires quantitative and fast testing. Furthermore, various flexible SERS substrates can be utilized in this system for toxic materials detection.

Double-crosslinked cellulose nanofiber based bioplastic films for practical applications.

While green bioplastic based on carbohydrate polymers have showed considerable promise, the methods typically used to prepare them in a single material have remained a significant challenge. In this study, a simple approach is proposed to fabricate high performance cellulose films composed of chemically and physically dual-crosslinked 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (DC TEMPO-CNFs). The hydroxyl groups of TEMPO-CNF suspensions were firstly crosslinked chemically with epichlorohydrin (ECH), and subsequently TEMPO-CNF matrices were crosslinked physically via the strong electrostatic interaction between carboxylate and Ca2+ ions. It was found that the optimized DC TEMPO-CNF films exhibit a good transmittance (90 %) and a high tensile strength (303 MPa). Furthermore, these DC TEMPO-CNF films revealed superior thermal stability and excellent water resistance compared to neat TEMPO-CNF films without crosslinked domains. We believe that these results will pave the way to preparing practical polysaccharide bioplastics with simple, environmentally-friendly manufacturing processes.

Vapor phase polymerization for electronically conductive nanopaper based on bacterial cellulose/poly(3,4-ethylenedioxythiophene).

Eco-friendly conductive polymer nanocomposites have garnered attention as an effective alternative for conventional conductive nanocomposites. Here, we report the fabrication and optimization of flexible, self-standing, and conductive bacterial cellulose/poly(3,4-ethylene dioxythiophene) (BC/PEDOT) nanocomposites using the vapor phase polymerization (VPP) method. Eco-friendly bacterial cellulose (BC) is used as a flexible matrix, and the highly conductive PEDOT polymer is introduced into the BC matrix to achieve electronic conductivity. We demonstrate that vapor phase polymerized BC/PEDOT composites exhibit more than 10 times lower sheet resistance (18 Ω/square) compared to solution polymerized BC/PEDOT (188 Ω/square). The resultant BC/PEDOT fabricated could be bent up to 100 times and completely rolled up without a notable decrease in electronic performance. Moreover, bent BC/PEDOT films enable operation of a green light-emitting diode (LED) light, indicating the flexibility and stability of conductive BC/PEDOT films. Overall, this study suggests a strategy for the development of eco-friendly, flexible, and conductive nanocomposite films.

Detection of nanoplastics based on surface-enhanced Raman scattering with silver nanowire arrays on regenerated cellulose films.

Plastic pollution has steadily become a global issue due to its ubiquity and degradation into micro and nanoparticles. Herein, we report the construction of surface-enhanced Raman scattering (SERS)-active array substrates with regenerated cellulose (RC) and plasmonic nanoparticles (AuNRs and AgNWs) via a simple vacuum-assisted filtration method using a silicon mask for rapid nanoplastic detection. The AgNWs/RC film exhibited a SERS intensity of crystal violet approximately six times higher than that of the AuNRs/RC film with a high enhancement factor of 1.8 × 107. Moreover, the AgNWs/RC film exhibits a better SERS activity for polystyrene nanoplastic detection than the AuNRs/RC film because the dense AgNW network structures are well suited for nanoplastic detection. The AgNWs/RC film can detect PS nanoplastics down to 0.1 mg/mL with a good reproducibility of the SERS signal. The low-cost, flexible, and highly sensitive AgNWs/RC films could provide an efficient and rapid SERS-based method for nanoplastic detection.

Surface-enhanced Raman scattering-active AuNR array cellulose films for multi-hazard detection.

In this study, we report a surface-enhanced Raman scattering (SERS)-active array film, which is based on regenerated cellulose hydrogels and gold nanorods (AuNRs), by combining a silicon rubber mask with a vacuum filtration method. This strategy enables the direct AuNR array formation on hydrogel surface with a precisely controlled number density. Moreover, the control of interparticle nanogap has been realized by the spatial deformation of hydrogels. A decrease in gaps between AuNRs deposited on hydrogels can result in SERS enhancement because 3D porous hydrogel structures turned into 2D closely packed hydrogel films during drying. In our experiments, SERS sensor arrays show excellent SERS activity to detect rhodamine 6 G and thiram down to 10 pM and 100 fM with competitive enhancement factors of 3.9 × 108 and 9.5 × 109, respectively. Importantly, the resultant SERS-active arrays with nine sensor units can efficiently detect nine different analytes on a single substrates at a time. Moreover, we demonstrate that physical bending has little effect on the SERS activity of flexible AuNR array hydrogel films, which indicates the high reproducibility of SERS measurement. This SERS array film has great potential to simultaneously detect multiple hazards for the practical application of SERS analysis.

Cellulose nanocrystal-coated TEMPO-oxidized cellulose nanofiber films for high performance all-cellulose nanocomposites.

High performance biopolymer films are of great interest as effective alternatives to non-biodegradable and petroleum-based polymer films. However, most natural biopolymer films possess weak mechanical and poor gas barrier properties, limiting their applicability. In this work, we developed all-cellulose nanocomposite films through a simple vacuum filtration process, using cellulose nanocrystals (CNCs) and 2,2,6,6-tetramethylpiperidine-1-oxy-oxidized cellulose nanofibers (TEMPO-CNFs). The TEMPO-CNFs were employed to construct a transparent, free-standing substrate matrix and the CNCs were used as a coating material to improve the mechanical and water vapor barrier properties of the final material. We have demonstrated that the top and bottom CNCs-coated TEMPO-CNF substrates (CNC/TEMPO-CNF/CNC) have excellent mechanical and good water vapor barrier properties. The resulting CNC/TEMPO-CNF/CNC films revealed a high tensile strength of 114 MPa and a low specific water vapor transmission rate (SWVTR) of 19 g∙mm/m2∙day. In addition, the CNC/TEMPO-CNF/CNC films were resistant to various solvents including water, ethanol, tetrahydrofuran (THF), and acetone. This type of high performance cellulose nanocomposite can be used as a renewable material for a broad range of potential applications.

Fabrication of Highly Conductive Porous Cellulose/PEDOT:PSS Nanocomposite Paper via Post-Treatment.

In this paper, we report the fabrication of highly conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/cellulose nanofiber (CNF) nanocomposite paper with excellent flexibility through post-treatment with an organic solvent. The post-treated PEDOT:PSS/CNF porous nanocomposite papers showed a lower sulfur content, indicating the removal of residual PSS. The electrical conductivity of PEDOT:PSS/CNF porous nanocomposite paper was increased from 1.05 S/cm to 123.37 S/cm and 106.6 S/cm by post-treatment with dimethyl sulfoxide (DMSO) and ethylene glycol (EG), respectively. These values are outstanding in the development of electrically conductive CNF composites. Additionally, the highly conductive nanocomposite papers showed excellent bending stability during bending tests. Cyclic voltammetry (CV) showed a Faradaic redox reaction and non-Faradaic capacitance due to the redox activity of PEDOT:PSS and large surface area, respectively. Electrochemical energy storage ability was evaluated and results showed that capacitance improved after post-treatment. We believe that the highly conductive PEDOT:PSS/CNF porous nanocomposite papers with excellent flexibility described here are potential candidates for application in porous paper electrodes, flexible energy storage devices, and bioengineering sensors.

An Organic/Inorganic Nanocomposite of Cellulose Nanofibers and ZnO Nanorods for Highly Sensitive, Reliable, Wireless, and Wearable Multifunctional Sensor Applications.

Organic and inorganic one-dimensional nanomaterials were synthesized and combined into a nanocomposite film for a wearable sensor. Reproducible ZnO nanorod (NR) synthesis was achieved by the addition of an appropriate amount of water. Cellulose nanofibers (CNFs) were used due to their porous matrix formation. The interconnected channels of brittle ZnO NRs were well-fabricated in the flexible network of CNFs. The surface morphology, thermal, and mechanical properties of the CNF/ZnO NR nanocomposite film were characterized. The interfacial interactions between these two nanomaterials were also studied. The nanocomposite film is sufficiently flexible so that it shows no electrical resistance changes even after repeated bending tests with a minimum bending radius of 1.5 mm. In addition, ZnO NRs with different lengths were synthesized. The composite of longer ZnO NRs and CNF showed 2.8 × 103 times higher photocurrent and responsivity performance. The humidity sensing performance of the composite was also suggested. The CNF/ZnO NR film shows reasonable electrical signal changes enabling the evaluation of a calibration curve. Finally, a smart band including a CNF/ZnO NR film sensor was fabricated and connected to a smartphone by Bluetooth. These results open an avenue for developing wearable sensors by overcoming the brittleness of inorganic materials.

Antibacterial poly (3,4-ethylenedioxythiophene):poly(styrene-sulfonate)/agarose nanocomposite hydrogels with thermo-processability and self-healing.

Recently, Near-infrared (NIR)-induced photothermal killing of pathogenic bacteria has received considerable attention due to the increase in antibiotic resistant bacteria. In this paper, we report a simple aqueous solution-based strategy to construct an effective photothermal nanocomposite composed of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) and agarose with thermo-processability, light triggered self-healing, and excellent antibacterial activity. Our experiments revealed that PEDOT:PSS/agarose was easily coated on both a 2D glass substrate and 3D cotton structure. Additionally, PEDOT:PSS/agarose can be designed into free-standing objects of diverse shape as well as restored through an NIR light-induced self-healing effect after damage. Taking advantage of strong NIR light absorption, PEDOT:PSS/agarose exhibited a sharp temperature increase of 24.5 °C during NIR exposure for 100 s. More importantly, we demonstrated that the temperature increase on PEDOT:PSS/agarose via photothermal conversion resulted in the rapid and effective killing of nearly 100% of the pathogenic bacteria within 2 min of NIR irradiation.

High-Performance Resistive Pressure Sensor Based on Elastic Composite Hydrogel of Silver Nanowires and Poly(ethylene glycol).

Improved pressure sensing is of great interest to enable the next-generation of bioelectronics systems. This paper describes the development of a transparent, flexible, highly sensitive pressure sensor, having a composite sandwich structure of elastic silver nanowires (AgNWs) and poly(ethylene glycol) (PEG). A simple PEG photolithography was employed to construct elastic AgNW-PEG composite patterns on flexible polyethylene terephthalate (PET) film. A porous PEG hydrogel structure enabled the use of conductive AgNW patterns while maintaining the elasticity of the composite material, features that are both essential for high-performance pressure sensing. The transparency and electrical properties of AgNW-PEG composite could be precisely controlled by varying the AgNW concentration. An elastic AgNW-PEG composite hydrogel with 0.6 wt % AgNW concentration exhibited high transmittance including T550nm of around 86%, low sheet resistance of 22.69 Ω·sq-1, and excellent bending durability (only 5.8% resistance increase under bending to 10 mm radius). A flexible resistive pressure sensor based on our highly transparent AgNW-PEG composite showed stable and reproducible response, high sensitivity (69.7 kPa-1), low sensing threshold (~2 kPa), and fast response time (20⁻40 ms), demonstrating the effectiveness of the AgNW-PEG composite material as an elastic conductor.

Micropatterning Silver Nanowire Networks on Cellulose Nanopaper for Transparent Paper Electronics.

Transparent microelectrodes with high bendability are necessary to develop lightweight, small electronic devices that are highly portable. Here, we report a reliable fabrication method for transparent and highly bendable microelectrodes based on conductive silver nanowires (AgNWs) and 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO)-oxidized cellulose nanofibers (CNFs). The AgNW-based micropatterns were simply fabricated on glass via poly(ethylene glycol) photolithography and then completely transferred to transparent TEMPO-CNF nanopaper with high bendability via vacuum-assisted microcontact printing (µCP). The AgNW micropatterns were embedded in the surface layer of TEMPO-CNF nanopaper, enabling strong adhesion to the nanopaper substrate. The resulting AgNW micropatterns on the TEMPO-CNF nanopaper showed an optical transparency of 82% at 550 nm and a sheet resistance of 54 Ω/sq when the surface density of AgNWs was as low as 12.9 µg/cm2. They exhibited good adhesion stability and excellent bending durability. After 12 peeling test cycles and 60 s sonication time, the sheet resistance of the AgNW networks embedded on TEMPO-CNF nanopaper increased by only ∼0.12 and ∼0.07 times, respectively. Furthermore, no significant change in electrical resistance was observed even after 3 bending cycles to nearly 90° and 500 cycles of 80% bending strain. Moreover, the AgNW patterns on TEMPO-CNF paper were successfully applied for constructing a transparent electric circuit as well as a solid-state electrochromic device. Overall, we proposed an effective way to fabricate AgNW micropatterns on transparent nanopaper, which can be expanded to various conductive materials for high-performance paper-based electronics.

Vacuum-assisted bilayer PEDOT:PSS/cellulose nanofiber composite film for self-standing, flexible, conductive electrodes.

Sustainable cellulose nanofiber (CNF)-based composites as functional conductive materials have garnered considerable attention recently for their use in soft electronic devices. In this work, self-standing, highly flexible, and conductive PEDOT:PSS-CNF composite films were developed using a simple vacuum-assisted filtration method. Two different composite films were successfully fabricated and then tested: 1) a single-layer composite composed of a mixture of PEDOT:PSS and CNF phases and 2) a bilayer composite composed of an upper PEDOT:PSS membrane layer and a CNF matrix sub-layer. The latter composite was constructed by electrostatic/hydrogen bonding interactions between PEDOT:PSS and CNFs coupled with sequential vacuum-assisted filtration. Our results demonstrated that the resultant bilayer composite film exhibited a competitive electrical conductivity (ca. 22.6Scm-1) compared to those of previously reported cellulose-based composites. Furthermore, decreases in the electrical properties were not observed in the composite films when they were bent up to 100 times at an angle of 180° and bent multiple times at an angle of 90°, clearly demonstrating their excellent mechanical flexibility. This study provides a straightforward method of fabricating highly flexible, lightweight, and conductive films, which have the potential to be used in high-performance soft electronic systems.

A Simple Silver Nanowire Patterning Method Based on Poly(Ethylene Glycol) Photolithography and Its Application for Soft Electronics.

Hydrogel-based flexible microelectrodes have garnered considerable attention recently for soft bioelectronic applications. We constructed silver nanowire (AgNW) micropatterns on various substrates, via a simple, cost-effective, and eco-friendly method without aggressive etching or lift-off processes. Polyethylene glycol (PEG) photolithography was employed to construct AgNW patterns with various shapes and sizes on the glass substrate. Based on a second hydrogel gelation process, AgNW patterns on glass substrate were directly transferred to the synthetic/natural hydrogel substrates. The resultant AgNW micropatterns on the hydrogel exhibited high conductivity (ca. 8.40 × 103 S cm-1) with low sheet resistance (7.51 ± 1.11 Ω/sq), excellent bending durability (increases in resistance of only ~3 and ~13% after 40 and 160 bending cycles, respectively), and good stability in wet conditions (an increase in resistance of only ~6% after 4 h). Considering both biocompatibility of hydrogel and high conductivity of AgNWs, we anticipate that the AgNW micropatterned hydrogels described here will be particularly valuable as highly efficient and mechanically stable microelectrodes for the development of next-generation bioelectronic devices, especially for implantable biomedical devices.

A Facile Approach for Constructing Conductive Polymer Patterns for Application in Electrochromic Devices and Flexible Microelectrodes.

We developed a novel strategy for fabricating poly(3,4-ethylenedioxythiophene) (PEDOT) patterns on various substrates, including hydrogels, via sequential solution procedure without multistep chemical etching or lift-off processes. First, PEDOT nanothin films were prepared on a glass substrate by solution phase monomer casting and oxidative polymerization. As a second step, after UV-induced poly(ethylene glycol) (PEG) photolithography at the PEDOT/PEG interface through a photomask, the hydrogel was peeled away from the PEDOT-coated glass substrate to detach the UV-exposed PEDOT region, which left the UV nonexposed PEDOT region intact on the glass substrate, resulting in PEDOT patterns. In a final step, the PEDOT patterns were cleanly transferred from the glass to a flexible hydrogel substrate by a direct-transfer process based on a second round of gelation process. Using this strategy, PEDOT patterns on ITO glass or ITO film were used to successfully fabricate an electrochromic (EC) device that exhibited stable electrochromic switching as a function of applied potential. Furthermore, PEDOT patterns on hydrogel were used to fabricate all organic, flexible microelectrodes with good electrical properties and excellent mechanical flexibility. Importantly, the conductivity of PEDOT patterns on hydrogel (ca. 235 S cm-1) described here is significantly higher than that previously reported (ca. 20-70 S cm-1). This approach can be easily integrated into various technological fabrication steps for the development of next-generation bioelectronics systems.